During the previous grant period, we focused on (a) effects of lung distention on fetal lung growth and development and (b) apoptosis in the fetal lung. The current project extends our observation on fetal lung distention and relates them to the clinical problem of congenital diaphragmatic hernia (CDH) and new methods of treating CDH prenatally. Congenital anomalies are a leading cause of neonatal death, with pulmonary hypoplasia the most common anomaly in infants dying the neonatal period. CDH, a major cause of pulmonary hypoplasia, occurs once in 2400 births and has a high mortality rate. Fetal lung growth depends primarily on physical, or mechanical factors, which influence lung growth by changes in lung distension, or stretch, a potent stimulus for diverse cellular effects. With CDH, pulmonary hypoplasia results from alteration of several of these factors. Occluding the fetal trachea distends the lung with fluid and stimulates lung growth, findings that have led to clinical efforts to treat CDH prenatally by tracheal occlusion. Although preliminary results have been encouraging, little is known about effects of tracheal conclusion on some aspect of lung development crucial to adequate pulmonary function, including quantitative lung morphology, the pulmonary vasculature, and lung water balance. Also, tracheal occlusion produces potentially adverse effects, such as decreases in surfactant and alveolar type II cells. Administration of the pesticide of the pesticide, nitrofen, to pregnant rats causes CDH and pulmonary hypoplasia in 60% of the fetuses; the condition resembles CDH in human infants. We propose to distend, by tracheal occlusion, the lungs in fetal rats with nitrofen-induced CDH and to study the effects on lung growth and maturation, on differentiation of the distal pulmonary epithelium, on quantitative pulmonary and vascular morphology. on lung water transport and on components of the cytoskeleton, which is involved in cellular transduction of mechanical stimuli. We will also examine effects on maternal (a) glucocorticoids, which accelerate lung maturation, but which may adversely affect septation and lung growth, and of (b) retinoic acid, which postnatally increases septation and reverses the decreased septation due to dexamethasone. We have shown that apoptosis is a normal process in fetal lung development. How3ever, because changes in lung distension have little effect on apoptosis, further studies of that process are not included in the current project. Results of the proposed studies will increase our knowledge of fetal pulmonary biology and provide new information that may have direct bearing on the clinical problem of CDH.